Final answer:
Emily is in the formal operational stage of cognitive development and is about 11 years and older, as she can conceptualize a classless society.
Step-by-step explanation:
When discussing a "classless society," Emily, who is able to imagine a hypothetical world with no differences in social classes, is most likely in the formal operational stage of cognitive development and about 11 years and older. This is the final stage in Piaget's theory of cognitive development, during which individuals are able to deal with abstract ideas and hypothetical situations.
In contrast to earlier stages, individuals in the formal operational stage can use abstract thinking to problem-solve and consider alternative solutions. This stage differs significantly from the concrete operational stage, where individuals can think logically only about real (concrete) events, and the preoperational stage where children can use symbols and engage in pretend play but cannot yet perform logical mental operations.